1. Field of the Invention
The invention relates to a method for determining slip between two component parts which transfer movement through contacting each other with friction engagement in a mechanism where the intensity of the frictional contact can be changed by altering the contact pressure.
2. Description of the Related Art
FIG. 3 shows a cone pulley belt contact gearbox, such as is known for example from DE 195 44 644 A1
A fist pair of cone pulleys with cone pulleys 4, 6 is mounted on a drive shaft 2, with the cone pulley 6 being formed integral with the shaft 2 and the cone pulley 4 being connected to the shaft 2 rotationally secured but axially displaceable through axial serrations. A further pair of cone pulleys with cone pulleys 10 and 12 is mounted on a further shaft 8 which is parallel to the shaft 2, whereby the cone pulley 10 is formed integral with the shaft 8 and the cone pulley 12 is connected to the shaft rotationally secured through axial serrations but axially displaceable.
The two pairs of cone pulleys 4, 6 and 10, 12 are looped round by a contact means 14 whose links come into friction engagement with the cone faces of the cone pulleys.
To adjust the transmission ratio the distance between the cone pulleys 4, 6 and 10, 12 is mutually displaceable. For this the relevant displaceable cone pulley is loaded with pressure from each of two pressure chambers, with an inner pressure chamber 18 serving to adjust the contact pressure between the contact means 16 and the pair of cone pulleys to a preliminary pressure which is dependent on operating parameters and which can be dependent on torque for example. To relax the pressure a spring 20 is mounted in the pressure chamber 18 or in a further pressure chamber 22. The further pressure chamber 22 is preferably used in order to adjust the distance between the cone pulleys 10 and 12.
To supply the pressure chambers with pressure there is a hydraulic medium pump 24 which supplies pressure controllable through the control valves 26 to the pressure chambers 18 which are biased with contact pressure, and supplies pressure to the adjustment chambers 22 through control valves 28.
Hydraulic medium which serves to cool the friction faces and for lubrication is introduced into the space between the cone pulleys for example through openings 30 in the shafts or in another suitable manner. The overflowing hydraulic medium is collected in a funnel 32 which leads into a return container 34 from which the hydraulic pump 24 sucks in the hydraulic medium.
The pressure chambers 18 of the two pairs of cone pulleys can like the adjustment chambers 22 of the two pairs of cone pulleys each be controlled through a common control valve.
The function and construction of the cone pulley belt contact gearbox described are known per se so that detailed explanation is not provided.
One problem which exists with cone pulley belt contact gearboxes of the kind mentioned is that the contact pressure between the friction faces of the cone pulley and the contact means should not be unnecessarily great since this leads on the one hand to an unnecessarily high energy consumption by the pump 24 and on the other leads to an unnecessarily high strain on the cone pulley belt contact gearbox overall. If the contact pressure is too low then there is the danger that the contact means slip on the cone pulleys which leads to a significantly increased wear. The measurement of the slip is a problem when not the speed of the contact means itself, but the active radii of the pairs of cone pulleys and their speeds are measured. The speeds of the pairs of cone pulleys are not a reliable measure for determining the slip. Since the slip can only be measured with comparative inaccuracy, and a state of slip is however dangerous for the durability of the gearbox, it is general to drive with a certain reserve contact pressure, i.e. with a contact pressure which is too high in itself.
The object of the invention is to provide a method for determining the slip between the contact means and the pairs of friction discs which leads with simple implementation to excellent results.
To achieve the foregoing objective, the method according to the invention uses a measurement of a value that corresponds to the power loss due to friction, also known as power dissipation, which occurs during the transfer of movement between the component parts. In this measurement, the power dissipation is determined in dependence on the contact pressure force, and a rise in the amount of power that is dissipated when the contact pressure force decreases is interpreted as slip.
The invention is based on the knowledge that the power dissipation due to friction which occurs between the contact means and the friction faces of the cone pulleys is comparatively slight substantially independent of the torque that is being transferred, provided no slip is present. As soon as slip occurs when the contact pressure drops, the level of power dissipation rapidly increases so that when the power dissipation or a value which corresponds to same, is measured the presence of slip is reliably detected.
The method according to the invention is suitable for all applications where movement is transferred through friction contact, such as toroidal gears, CVT gearboxes in general or other transmission systems.